The most important one of requirements of a next-generation wireless access system is to support a high data transfer rate. To achieve this, various technologies such as Multiple Input Multiple Output (MIMO), Cooperative Multiple Point Transmission (CoMP), relay, etc. have been developed and studied.
Although downlink and uplink bandwidths are different from each other, a conventional wireless communication system typically uses one carrier. For example, a wireless communication system having one carrier for each of downlink and uplink and symmetry between downlink and uplink bandwidths may be provided based on a single carrier.
However, in order to guarantee a broadband bandwidth capable of satisfying a higher data transfer rate considering that frequency resources are saturated, carrier aggregation (CA)/multiple cells technology has been proposed, which is designed for each bandwidth to satisfy basic requirements capable of operating an independent system and aggregates a plurality of bandwidths using a single system.
In this case, a bandwidth-based carrier capable of being independently operated may be referred to as a component carrier (CC). In order to support the increasing transmission capacity, a bandwidth of the latest 3GPP LTE-A or 802.16m has been continuously extended up to 20 MHz or more. In this case, one or more component carriers (CCs) are aggregated to support a broadband. For example, provided that one CC supports a bandwidth of 5 MHz, 10 MHz or 20 MHz, a maximum of 5 CCs are aggregated to support a system bandwidth of up to 100 MHz.